1. Field of the Invention
The present invention relates to a nitride semiconductor laser element, and more particularly relates to a nitride semiconductor laser element having a protective film on an end face of the cavity.
2. Background Information
With a nitride semiconductor laser element, end faces of the cavity formed by RIE (reactive ion etching) or cleavage has a narrow bandgap energy, so absorption of the exiting light occurs at the end face, this absorption generates heat at the end face, and problems such as a short service life are encountered in trying to obtain a high-output laser. Consequently, there has been proposed, for example, a method for manufacturing a high-output semiconductor laser in which a silicon oxide or nitride film is formed as a protective film on the cavity end face (see, for example, Japanese Laid-Open Patent Application H9-283843).
Meanwhile, conventional nitride semiconductor laser elements have employed a method in which the thickness of the protective film formed on the cavity end face is varied according to the density of the emitted light in order to suppress variance in device characteristics from chip to chip (see, for example, Japanese Laid-Open Patent Application 2006-228892). Also, it has been proposed that a stripe structure is employed inside the cavity, unimodality of FFP (Far Field Pattern) is achieved, for example, an SiO2 film is used as a protective film, and the thickness of the protective film is varied for each stripe (see, for example, Japanese Laid-Open Patent Application 2002-329926).
A method has been proposed for forming an end face coating film via an adhesive layer on a cavity end face in order to suppress the end face deterioration in nitride semiconductor laser elements (see, for example, Japanese Laid-Open Patent Application 2002-335053).
However, as the output of semiconductor lasers has risen, there has been a need for further improvement to structures related to the exit of light from a cavity end face. That is, there is a need for a structure with which the adhesion of the protective film is maximized without imparting stress to the active layer, for example, according to the performance, etc., thereof, while still being able to prevent degradation of the protective film during drive of the laser element.
Also, there is increasing demand for nitride semiconductor laser elements that are compact and have low output, which are used to reproduce next-generation optical disks. As the reflectance of the cavity end face of a nitride semiconductor laser element rises, the load on the cavity end face becomes large despite the low output. Consequently, just as with a high output semiconductor laser, there is need for improvement to the structure related to the exit of light from the cavity end face.